SAVE $400: As of July 11 (the first day of Prime Day), the iRobot Roomba s9+ is $599.99 for Prime members. That's 40% off its usual cost of $999.99 and its lowest price to date.

Opens in a new tab Credit: iRobot iRobot Roomba s9+ (opens in a new tab) $599.99 at Amazon (save $400) Get Deal (opens in a new tab)

Several excellent robot vacuums are at record-low pricing this Prime Day. Between almost all of Roborock's newest and second-newest collections on sale and a Roomba under $150, it's hard to pick a favorite.

But fine, twist our arm: We have to hype Amazon's unprecedented deal on the Roomba s9+, which puts the strongest Roomba and the best robot vacuum for carpet at $599.99 — that's $400, or 40%, off its usual price of $999.99. This isn't to say that the s9+ never goes on sale, but $799.99 is typically its best sale price. $599.99, on the other hand, is the lowest it's ever been.

SEE ALSO: The best Prime Day products to shop

Though the s9+ (the plus signifies the inclusion of an automatic emptying dock) isn't iRobot's newest release, it holds its own against the newest j7+ for several reasons. First and foremost, the s9+ is much more of a beast when it comes to suction power. According to iRobot's website, it produces 40 times the suction power of the Roomba 600 series, whereas the j7+ has 10 times that suction power. That, plus a dual rubber brush that's 30% wider than other Roombas, allows it to dig into plush carpeting and grab more debris and pet hair.

As the only D-shaped robot vacuum, the s9's flat edge can fit into corners where a circular vac and its brushes may miss.

Like the j7+, the s9+ maps out your home and internalizes the layout for the cleaning of specific rooms or specific areas, like under the kitchen table. (Unlike the j7+, it can't recognize small obstacles like phone chargers or pet waste.) The self-empty dock holds at least 60 days' worth of debris before you need to think about emptying.